Field of the Present Invention
The present invention relates generally to electromagnetic tomography, and, in particular but not exclusively, to 4D electromagnetic tomography for producing fused anatomical-functional images of biological objects.
Background
Electromagnetic tomography (EMT) is a relatively recent imaging modality with great potential for biomedical applications, including a non-invasive assessment of functional and pathological conditions of biological tissues. Using EMT, biological tissues are differentiated and, consequentially, can be imaged based on the differences in tissue dielectric properties. The dependence of tissue dielectric properties from its various functional and pathological conditions, such as blood and oxygen contents, ischemia and infarction malignancies has been demonstrated.
Two-dimensional (2D) and three-dimensional (3D) EMT systems and methods of image reconstruction have been developed over the last decade or more. Feasibility of the technology for various biomedical applications has been demonstrated, for example, for cardiac imaging and extremities imaging.
Complexity of EM Distribution within an Imaging Chamber: the Need to Diminish Effect from Boundaries.
As in any biomedical imaging, the classical EMT imaging scenario consists of cycles of measurements of complex signals, as scattered by a biologic object under study, obtained from a plurality of transmitters located at various points around the object and measured on a plurality of receivers located at various points around the object. This is illustrated in FIG. 1. As recounted elsewhere herein, the measured matrix of scattered EM signals may then be used in image reconstruction methods in order to reconstruct 3D distribution of dielectric properties of the object, i.e., to construct a 3D image of the object.
Generally, it is very important for image reconstruction to precisely describe a distribution of EM field with an imaging domain. The distribution of EM field with an imaging chamber is a very complex phenomenon, even when there is no object of interest inside.
There are also boundary problems arising from restricted volume of an imaging domain which needs to be taken into account or efforts made in order to diminish boundaries effect.
There are different ways for diminishing boundary effects. For example, boundary effects may be diminished by using an absorptive material(s), as described in U.S. Pat. No. 7,239,731, or boundary effects may be diminished by increasing the absorptive properties of a matching solution, conserving a sufficient level of the signal on receivers as described herein (see block “Attenuation vs boundary problem assessment block” in FIG. 11).
Recent Trends in Biomedical Imaging: Fused Images of Multi-modalities System.
Medical imaging plays a significant role in advances in modern non-invasive diagnostics, treatment planning and post-treatment follow-up studies. Recently medical imaging has expanded into dual- and multi-modality fusion of morphological/anatomical (for example, CT and MRI) and functional (for example, FDG-PET and DCE-MRI) imaging modalities. This significantly improves the diagnostic power while simultaneously increasing the cost of already expensive medical imaging devices and investigations.
An initial approach of software based image fusion suffered from significant problems caused by different patient position, motion, involuntary movement of internal organs. This lead to a fusion of different imaging modalities into a single imaging setting, rather than fusion of the images within a post-imaging procedure. One of the first dual-imaging system/combined PET/CT was developed at the University of Pittsburg Medical School. The combined PET/CT scanner was designed primarily for applications in clinical oncology. The first combined commercial PET/CT system approved by the FDA was manufactured by CTI PET Systems in 2000, shortly followed by GE Medical systems and Philips. It is now agreed that PET/CT is significantly more accurate than PET alone for the detection and localization of tumors and PET/CT is superior to PET alone in terms of sensitivity, specificity and accuracy, mainly because of the detection of new lesions. In addition, combined PET/CT allows for considerable gain of examination time within a single session.
Following the introduction of the PET/CT combination, various other combinations of different imaging modalities have been reported. Combined SPECT/CT has proven useful for cardiac, oncologic and neurologic applications. Combined 3D echocardiography and myocardial perfusion SPECT has been used for cardiac stress testing. MRI/CT image fusion is used in computer assisted surgery. The feasibility of fused whole-body MRI/FDG-PET for the evaluation of patients with cancer has been demonstrated. Authors of one study stated that “because some malignant tumors do not show increased glucose metabolism, the additional information provided by MRI brings substantial benefits.”
Further on, dual-modality fused imaging has expanded into multi-modality imaging. Multi-modality fusion of morphological (CT and MRI) and functional (FDG-PET and DCE-MRI) images has been shown combining the three most clinically used tomographic imaging modalities (CT, MRI and PET) in treatment planning, navigation and follow up for radiofrequency ablation of tumors.
There is a recent trend in the development of medical imaging devices specifically dedicated for imaging of a certain diseases, for example cancer. This is significantly different from the concept of previous all-purpose system. For example, one study reported the construction of PET/CT scanner dedicated specifically for breast imaging. In this study, an FDG tracer was used and the duration of an imaging session was 12.5 min per breast.
As set forth above, multi-modality imaging significantly improves diagnostic power. However, it simultaneously increases the cost of already-costly medical devices. Further, multi-modalities imaging systems are very bulky and are not applicable for mobile settings. Thus, a need exists for systems, methods and approaches that provide fast, cost-efficient fused anatomical-functional imaging applicable, preferably for mobile settings.